Magneto-rheological elastomers (MREs) are elastomer composites that can be used in a variety of applications for vibration isolation and energy dissipation. The basic principle of MREs is that manipulating the magnetic field exerted on the MRE can control their stiffness and their damping capacity. Increasing the magnetic field inside the MRE causes the stiffness of the MRE to increase. Without wishing to be bound by any particular theory, it is believed that an increase in MRE damping capacity will be coupled to an increase in stiffness. Thus, by matching the magnetic field in the MRE to the external forces acting on the MRE, it is possible to regulate the MRE's stiffness to best tune a response to vibrational forces exerted on the MRE.
An MRE is comprised of an elastomeric host or carrier material filled with iron or other magnetizable particles. The addition of magnetizable particles to the carrier produces an elastomer whose mechanical properties can be rapidly and continuously controlled with an applied magnetic field. The strength of an MRE can be characterized by its field-dependent modulus (modulii). A MRE is a field-controllable material with tunable stiffness and damping characteristics, which makes it useful for vibration isolation and damping applications.
If a magnetic field is applied to the elastomer during curing and the particles are able to move through the host medium, the magnetic particles orient into chains or columns parallel to the direction of the magnetic field (Ginder, J. M., Nichols, M. E., Elie, L. D., Tardiff, J. L., (1999), “Magnetorheological Elastomers: Properties and Applications, Smart Materials Technologies,” Ed. by M. Wuttig, Proc. of SPIE Vol. 3675, 131–137). As the elastomer cures, the aligned magnetic particles are locked into place and are ready for activation when installed in a device that can energize the material with a magnetic field. Under the influence of a magnetic field, dipole moments are induced in the magnetic particles resulting in an increase or decrease in stiffness and damping of the composite material depending on magnetic field strength.
A variety of elastomers have been proposed as carrier materials for magneto-rheological elastomers. Ginder et al. describe MREs having micrometer-sized carbonyl iron particles embedded in natural rubber (Ginder, J. M., Nichols, M. E., Elie, L. D., Tardiff, J. L., (1999), “Magnetorheological Elastomers: Properties and Applications, Smart Materials Technologies,” Ed. by M. Wuttig, Proc. of SPIE Vol. 3675, 131–137). Shiga et al identify rubber as a carrier material (English abstract of Japanese publication 04-266970, English abstract of Japanese publication 05-025316A). Elie et al (U.S. Pat. No. 5,974,856) list natural rubber, silicone, polybutadiene, polythethylene, polyisoprene, polyurethane and the like as elastomeric carrier materials. Viera et al. (WO 02/09015) list natural rubber, silicone, polybutadiene, polyethylene, styrene butadiene rubber (SBR) nitrile rubber, polychloroprene, polyisobutylene, synthetic polyisoprene, and blends thereof as elastomeric carrier materials. Ottaviani et al. (U.S. Publication 2004/0074061) list elastomeric polymer matrices of polyalpha-olefins, natural rubber, silicone, polybutadiene, polyethylene, polyisoprene, polyurethane, and the like.
MRE-based devices can be used in mechanical systems to mitigate shock events and in civil infrastructure to mitigate seismic and natural hazards as well as to protect infrastructure from man-made hazards. This family of devices can be used in optical applications, mechanical systems, automotive engine mounts, suspension systems, rotating shaft vibration isolation, sensitive equipment mounts, and manufacturing automation systems that require vibration isolation to improve production performance. Any system that is subjected to random shock events can benefit from a controllable/tunable vibration isolator and energy dissipater. The device of the present invention combines a controllable MRE device, shaped to any geometry, with a feedback control system to insure the desired device response to a given shock event is optimized for maximum damping and vibration isolation.
MRE-based devices have been used in automotive bushings to improve vehicle ride and handling performance. Watson (U.S. Pat. No. 5,609,353). Watson discloses generating an electrical current to a single electrocoil based on a transmission state signal such that the bushing stiffness is related to the transmission state. However, the bushings in Watson are limited to a magnetic field in the radial direction generated by a single electrocoil. Thus, the MRE device is constrained to damping vibration between annular cylinders. The present invention addresses the need in the art for MRE devices useful for various geometries and a variety of applications beyond automotive bushings. The present invention addresses this need, in part, by using multiple magnetic nodes such that the MRE can be used to damp vibration and dissipate energy from any direction that the external force is applied.